The proposed research will explore the hypothesis that sudden infant death syndrome (SIDS) results from a relative or absolute deficiency in magnesium (Mg) following rapid growth on a cow's milk formula; this is of unbalanced mineral composition for the human infant. Mediators, including histamine, may be released during plasma Mg ions/Ca ions imbalance; an exaggerated response resulting in anaphylactoid shock and death might occur in a young infant with low adrenal corticoids, during cold and hypoglycemia. The group of mothers contributing a disproportionately high percent both of low birth weight infants and SIDS infants, economically disadvantaged young urban women of high parity for their ages, will be studied immediately postpartum. Controls will be well nourished women matched for age and parity. Infants up to 6 months of age presenting with nonspecific symptoms suggestive of Mg deficiency of "premonitory signs" of SIDS (neuromuscular hyperirritability, apnea, pallor, eye signs, or rigidity), will be studied. Symptomatic infants of low weight at birth who more than doubled their weight in 3 to 4 months on a cow's milk formula will be most suspect. Controls will be full term, asymptomatic infants growing at a normal rate that will approximately double their birth weights in 6 months. The magnesium status of all postpartum women and infats will be assessed by means of parenteral magnesium-load tests, cation analyses, and other appropriate biochemical parameters. Also, cord blood, secundines, and stillborn fetus will be studied. Home-cooked diets and foods will be analyzed for cations. The aims are to obtain control data of cation balance in the normal puerperium and early infancy as well as data from poorly nourished young mothers and symptomatic infants. It is hoped that recommendations concerning the requirements for magnesium during pregnancy and early infancy can then be made, with delineation of some problems attending pregnancy and early infancy that may be related to ion imbalance or deficiency. It should become clear whether or not SIDS results from magnesium deficiency. Recommendations will be made for the correction and prevention of problems caused by ion imbalance.